This invention relates to a socket for a lattice shaped arrangement type IC package having a group of IC lead wires.
In general, this type of socket is for an IC package arranged in a lattice shape including a group of IC lead wire holes arranged in a lattice shape and a group of contacts for contacting IC lead wires placed under the group of IC lead wire holes corresponding thereto and arranged in a lattice shape as disclosed in, for example, Japanese Patent Early Laid-open Publication No. 58-150281. It is a common structure for them that contacting piece portions (which form contacting points with IC lead wires) of all contacts arranged in a lattice shape as mentioned above are arranged on vertical lines or lateral lines of the lattice-shaped arrangement so that the displacement for the contact engaging or release of the afore-mentioned contacts is performed in the direction of the vertical lines or lateral lines (within a space corresponding to a pitch of adjacent IC lead wires).
The IC lead wires of the IC lead wires for the IC package arranged in a lattice shape are arranged at very narrow pitches. In recent years, the tendency is toward the lead wire pitches becoming much narrower and the lead wires being arranged in higher density in a lattice shape.
Heretofore, for example, lattice shapedly arranged IC package having an International Standard pitch of 2.54 mm (space between adjacent IC lead wires) have been widely used. In recent years, a lattice shapedly arranged IC package having a pitch of 1.27 mm or less was provided. This is less than one half of the International Standard. Therefore, suitable IC sockets are demanded.
However, if an IC socket having the above-mentioned structure is applied to an IC package in which the lead wire pitch is reduced to one half, each contact for contacting each of the IC lead wires is required to be arranged within the space (within a space between adjacent IC lead wire holes having a 1.27 mm pitch) of the afore-mentioned 1.27 mm pitch between the IC lead wires. In addition, an amount of displacement enough for contact engaging and releasing in the 1.27 mm pitch must be provided. This is a very difficult condition to satisfy in view of manufacture.
Known contacts of the above-described type are the single spring type in which a contact pressure is given to one side of IC lead wires and also of the double spring type in which a contact pressure is given to both sides of IC lead wires. In either case, the contacting piece portion is usually warped or bent in a reversed L-shape, U-shape and the like, or otherwise the whole contacting piece is inclined to obtain a satisfactory elasticity. Naturally, the contact itself has a required width in the longitudinal direction. In addition, a back space must be formed behind the contact for permitting displacement for contact engaging or releasing of the contact. Furthermore, it is required to provide a space and a partition wall between the adjacent contacts for insulation. While, in a retractable socket of low resistance in which the IC lead wire is moved from the release position to the contact engaging position with respect to a contact and held between adjacent contacts or urged against the contact, a moving stroke of the IC lead wire is required.
In the conventional sockets having the above-described structure, the mounting width (a space enough for mounting the contact itself) of the contact itself and the back space for displacement and, in addition, the partition wall, etc. for insulation must be provided within a space corresponding to the IC lead wire pitch. However, it becomes more and more difficult to satisfy the above requirements within the space corresponding to the IC lead wire pitch which is coming to be much narrower as mentioned above. Further, in both of the single spring type socket and the double spring type socket, miniturization is restricted in view of the necessity for preventing deformation and obtaining a proper elastic displacement. Particularly, in a zero insertion type IC socket in which a contacting piece forming the contact is required to be spread wider, a wider back space is required. On the other hand, in a socket of the type in which the IC lead wire is moved between the contact engaging position and the release position, a moving stroke of the IC lead wire is required. In such a case, there are possibilities that the conventional types are not usable.